1. Field of the Invention
The present invention generally relates to cleaning semiconductor processing chambers, and more particularly, to systems and methods for cleaning a semiconductor processing chamber using a remote plasma source.
2. Description of the Related Art
Conventional techniques for removing undesired deposits, films, and residues from the surfaces of hardware located inside a processing chamber typically involve so-called direct plasma clean methods. In such methods, cleaning gases are injected and plasmas are generated directly within the processing chamber. Plasma-activated species then react with the unwanted deposits to form a volatile by-product that is pumped out of the processing chamber. These cleaning methods are desirable in that they reduce the potential for contamination by removing deposits that may shed particles on the substrate being processed. Furthermore, a more stable processing environment may be realized by removing accumulated materials that may interfere with the control of processing conditions. Direct plasma clean methods, however, have the disadvantage in that plasma generated ions continuously bombard internal surfaces of the processing chamber and can cause damage to associated hardware, such as susceptors, heater blocks, lift pins, gas lines, viewports, showerheads, thermal shields, susceptors, and temperature measuring probes such as optical pyrometers and thermocouples. In addition, direct plasma clean methods may not completely clean peripheral areas of the processing chamber or areas that are difficult to access such as underneath susceptors, places around robotic parts such as lift pins, or within gas distribution showerheads.
In order to overcome these disadvantages, remote plasma clean methods have been developed to avoid many of the problems encountered with direct plasma cleaning. In a Remote Plasma Clean (RPC) process, a plasma is ignited from gases fed into a chamber that is located remotely from the processing chamber. Plasma-activated species from the RPC chamber then flow through a delivery line towards the processing chamber. Because the plasma is generated remotely and in a separate compartment from the processing chamber, there is less opportunity for ion bombardment and plasma radiation to damage hardware within the processing chamber. Once delivered to the processing chamber, the activated species can then react with the unwanted deposits and residues, and the volatile by-products can be removed from the processing chamber.
Although remote plasma cleaning methods alleviate many of the problems encountered with direct plasma cleaning, there are still many challenges to be addressed. One such challenge is the phenomenon of recombination, which occurs when activated species generated in the RPC chamber recombine while flowing to the processing chamber. The activated species may comprise, for example, neutral fluorine radicals, which can recombine into a non-reactive form. Of course, not all the radicals recombine on their way to the processing chamber, but any recombination that does occur lowers the overall efficiency of the remote cleaning process, and requires an increased flow of feed gases to the RPC chamber to make up for the loss of efficiency. This recombination of activated species is undesirable because the cleaning gas is expensive, and disposing of the chemically inactive recombined radicals can be environmentally unfriendly.
One cause of excessive recombination occurs when the gas delivery system exhibits a low gas conductance. A low gas conductance results in higher pressures in the delivery system, which increases the likelihood of a collision between two (rarely more) activated species to form a non-reactive molecule. A low conductance delivery system can also substantially increase the operating pressure within the RPC chamber. This pressure is often referred to as backpressure from the point of view of the RPC chamber, since this is the pressure against which the remote plasma source is forced to deliver activated species. High backpressure in the RPC chamber requires high RF plasma power to generate sufficient plasma-activated species for effective clean rates. This high power consumption results in low cleaning efficiencies and affects the overall cost of performing the clean.
Another problem associated with RPC processes occurs when gases present during substrate processing travel from the processing chamber to the RPC chamber through the delivery system in a reverse direction. This diffusion of process gases into the RPC chamber is undesirable due to the potential for the RPC chamber to become contaminated. Moreover, an open RPC delivery system presents a larger deposition volume (represented by the volume of the delivery line and RPC chamber). This increase in volume may influence and interfere with processing conditions in the processing chamber (e.g., chamber pressure and gas flows) during substrate processing.
Other problems typically encountered with remote plasma cleaning operations involve the difficulty in cleaning various regions of the processing chamber. For example, the plasma-activated species may be unable to reach areas underneath the susceptor, places around robotic parts such as the lift pins used to raise and lower the substrate during substrate transport, and cavities within the showerhead used to supply and distribute process gases to the processing chamber. Furthermore, chambers adjacent to the processing module, such as substrate transfer chambers, vacuum loadlocks, and the isolation doors between them are typically not addressed by conventional RPC processes. Further problems occur when plasma-activated species from the RPC chamber react with materials that comprise the deposition gas delivery system (materials such as stainless steel), thereby causing some of those materials to flow into the processing chamber and contaminate the substrate being processed. Still further problems involve determining the point at which the cleaning process is complete.
Therefore, in light of the deficiencies with conventional approaches, there is a need for systems and methods that can efficiently and effectively clean semiconductor processing chambers using improved remote plasma cleaning techniques.
Aspects of the present invention provide a Remote Plasma Cleaning (RPC) system for cleaning the interior of a separate processing chamber or reactor. The RPC system may include a RPC chamber coupled to a gas supply and power supply for igniting and sustaining a cleaning plasma within the RPC chamber. The RPC plasma may be generated from a mixture of gases including, but not limited to, NF3 and Ar. A high conductance delivery system couples the RPC chamber to a processing chamber and enables activated species to flow from the RPC chamber to the processing chamber. The activated species are preferably introduced into the processing chamber via a dedicated inlet port, such as an opening formed in a wall of the processing chamber. The inlet port substantially increases the conductance of the RPC delivery system compared to delivering the RPC gas through a conventional showerhead, reducing the backpressure experienced by the RPC chamber. The RPC chamber may also be arranged close to and below the processing chamber to reduce the length (and further increase the conductance) of the RPC delivery system, while allowing unobstructed access to a top portion of the processing chamber. These aspects of the present invention enable the conductance of the delivery system to be greater than about 40 liters per second when measured with a process chamber pressure greater than or equal to 1 Torr, and a RPC feed gas flow rate of about 2,000 sccm. These aspects also allow the power supplied to the RPC chamber to be maintained at a level less than about three kilowatts (3 kW).
Other aspects of the present invention incorporate an isolation valve in the delivery system for selectively isolating the RPC chamber from the processing chamber. For example, the isolation valve may be configured to isolate the RPC chamber during substrate processing in order to prevent the additional volume of the RPC chamber from interfering with processing conditions and to prevent process gases from the processing chamber from contaminating the RPC chamber. The isolation valve may then be opened to allow cleaning gases from the RPC chamber to flow through the delivery system into the processing chamber. A gate valve may also be used as part of a compound valve to protect sensitive components within the isolation valve, such as sealing components, from exposure to activated species when the isolation valve is in an open position. An optical baffle may also be disposed within the output tube of the RPC chamber to further reduce the extent to which sensitive components of the isolation valve are exposed to radiation and ion bombardment emitted from the RPC chamber.
In a first embodiment of the present invention, activated species from the RPC chamber are introduced into the processing chamber via a first and a second inlet port that are preferably spaced apart so as to introduce activated species into different portions of the processing chamber. The inlet ports may be advantageously coupled to the same RPC chamber by, for example, coupling the RPC delivery system to a manifold that supplies each inlet port. For processing chambers having dual processing stations, for example, the inlet ports may be spaced apart such that the first inlet port introduces activated species to a first processing station and the second inlet port introduces activated species to a second processing station. Cleaning gases and volatile by-products from the cleaning process may then be exhausted from the processing chamber via an exhaust port. In this embodiment of the present invention, an exhaust port may be approximately equally spaced between the first and the second inlet ports in order to provide substantially uniform exhaust of volatile by-products from both processing stations. The first embodiment of the present invention may further include flow channels formed in the processing module that enable cleaning gases to flow underneath the susceptor to clean robotic parts, lift pin assemblies and other components and surfaces located underneath the susceptor. Other inlet ports coupled to the processing chamber, such as the showerheads and process gas delivery lines used to supply process gases during substrate processing, may be cleaned by flowing a portion of the cleaning gas through the showerheads and their associated delivery lines.
In a second embodiment of the present invention, activated species are introduced into the processing chamber and volatile by-products are exhausted from the processing chamber via a coaxial inject/exhaust assembly. The coaxial inject/exhaust assembly may include an inner tube coupled to the RPC delivery system for delivering activated species to the processing chamber, and an outer tube coupled to an exhaust system for exhausting gases from the processing chamber. In this embodiment, the coaxial inject/exhaust assembly may be disposed in a central portion of the processing chamber, such as between a first and a second processing station. A plurality of exhaust ports may then be arranged around a peripheral portion of the processing chamber to draw activated species from the central portion toward the peripheral portion to affect cleaning of the interior of the processing chamber. Each exhaust port may also be coupled to a flow channel that directs activated species from the RPC chamber underneath the susceptor and susceptor support toward interior cavities to clean surfaces and components located underneath the susceptor and susceptor support before the activated species (and cleaning reaction by-products) are exhausted via the outer exhaust tube of the coaxial inject/exhaust assembly. These flow channels advantageously allow activated species to clean the underneath portions of the susceptor support, the lift pins and associated robotic parts as the activated species flow through the flow channels toward the coaxial inject/exhaust assembly.
Other embodiments of the present invention enable endpoint detection of a cleaning process to be performed by igniting a second low power (e.g., less than about 800 W) plasma in the process chamber from the activated species of the RPC chamber. Endpoint detection may be performed by monitoring the emission lines of species within the second plasma, and may include further signal processing that involves taking appropriate ratios of those emission lines.